Polygraph

A
polygraph or lie detector is a device which measures and records
several physiological variables such as blood pressure, heart rate, respiration and skinconductivity while
a series of questions is being asked, in an attempt to detect lies. A polygraph
test is also known as a psychophysiological detection of deception (PDD)
examination.

A
typical polygraph procedure starts with a pre-test interview designed to establish
a connection between the tester and the testee and to gain some preliminary information
which will later be used for control questions (see below). Then the tester will
explain the polygraph, emphasizing that it can detect lies and that it is important
to answer truthfully. Then a "stim test" is often conducted: the testee is asked
to deliberately lie and then the tester reports that he was able to detect this
lie. Then the actual test starts. Some of the questions asked are irrelevant ("Are
you 35 years old?"), others are "probable-lie" control questions that most people
will lie about ("Have you ever stolen money?") and the remainder are the relevant
questions the polygrapher is really interested in. The different types of questions
alternate. The test is passed if the physiological responses during the probable-lie
control questions are larger than those during the relevant questions. If this
is not the case, the tester attempts to elicit admissions during a post-test interview
("Your situation will only get worse if we don't clear this up"). These admissions
are the main goal of the test.

The
accuracy of polygraph tests is a matter of considerable controversy. While some
claim the test to be accurate in 70% - 90% of the cases, critics charge that rather
than a "test", the method amounts to an inherently unstandardizable interrogation
technique whose accuracy cannot be established. Polygraph tests have also been
criticized for failing to catch actual spies such as Aldrich
Ames, who passed two polygraph tests while spying for the Russians.

Several
countermeasures designed to pass polygraph tests have been described, the most
important of which is never to make any damaging admissions. Additionally, several
techniques can be used to increase the physiological response during control questions.
In an interview, Ames was asked how he passed the polygraph test. His response
was that when told he was to be polygraphed he asked his Soviet handlers what
to do, and was quite surprised that their advice was simply to relax when being
asked questions, which he did.

The
polygraph machine was tested for the first time on February 2, 1935 when Leonard Keeler conducted
the experiment in Portage, Wisconsin.
They were often used by employers in an attempt to screen out dishonest job applicants,
but this practice was outlawed for most private employers in 1988. Many government
agencies still apply routine lie detector tests to screen all employees. While
lie detector tests are commonly used in police investigations, no defendant or
witness can be forced to undergo the test. A US Supreme
Court decision of 1998 left it up to the individual jurisdictions whether
polygraph results could be admitted as evidence in court cases.

Polygraphs
are not considered reliable evidence and are not employed by police forces in
most European jurisdictions.

A
related technique called the bogus
pipeline involves connecting a person to a non-functioning polygraph (or other
sophisticated looking device), and convincing him or her that the device can detect
deception. One example might be a metal colander placed on the subject's
head, with non-functional wires leading to a Xeroxphotocopier. When a lie is
suspected, the copy button could be pushed - thus spitting out a piece of paper
with the words "LIE DETECTED". There have not been any confirmed examples of this
actually being used by a police department1.

Studies
have shown that, compared to control conditions, individuals connected to a bogus
pipeline, who believe the pipeline is able to detect lies, are more likely
to provide truthful responses2. If the
subject is aware of the bogus nature of the pipeline, the test has much less utility.